Water-soluble phenylazoaminonaphthol sulphonic acid dyestuffs

ABSTRACT

A water-soluble monoazo dyestuff which, in the form of the free acid, corresponds to the formula ##STR1## wherein R 1  denotes alkyl which can be mono-substituted by chlorine, hydroxyl, C 1  to C 4  alkoxy, cyano, phenyl or tolyl, cyclohexyl which can be optionally substituted by C 1  -C 4  alkyl, phenyl, C 1  -C 4  -alkyl phenyl, chlorophenyl, bromophenyl, trifluoromethylphenyl or naphthyl, alkenyl or benzenesulphonyl which can be substituted by fluorine, chlorine, bromine, trifluoromethyl, C 1  -C 4  -alkyl or C 1  -C 4  -alkoxy, 
     R 2  denotes hydrogen, C 1  -C 4  -alkyl which can be substituted by hydroxyl, cyano, formylamino, C 1  -C 4  alkylcarbonylamino or benzoylamino which in turn can be substituted by methyl, chlorine, bromine or trifluoromethyl; cyclohexyl or phenyl which can be substituted by C 1  -C 4  alkyl, C 1  -C 4  -alkoxy, chlorine, bromine or trifluoromethyl and 
     R 3  denotes hydrogen or C 1  -C 4  -alkyl and a process for the preparation of such water-soluble mono-azo dyestuff. The dyestuffs according to the invention are suitable for dyeing natural and synthetic fibre materials, for example for dyeing wool or polyamide fibres, in level, deep red to violet shades with very good fastness to light, wet processing and perspiration.

The invention relates to water-soluble monoazo dyestuffs which, in the form of the free acid, correspond to the formula ##STR2## wherein

R₁ denotes optionally substituted alkyl, optionally substituted cyclohexyl, optionally substituted phenyl or naphthyl, alkenyl or optionally substituted benzenesulphonyl,

R₂ denotes hydrogen, optionally substituted C₁ -C₄ -alkyl, cyclohexyl or optionally substituted phenyl and

R₃ denotes hydrogen or C₁ -C₄ -alkyl.

The sulphonic acid group is preferably in the m-position or p-position relative to the hydroxyl group.

Suitable substituents R₁ are C₁ -C₈ -alkyl which is optionally monosubstituted by chlorine, hydroxyl, C₁ -C₄ -alkoxy, cyano, phenyl or tolyl, C₂ -C₄ -alkenyl, cyclohexyl, C₁ -C₄ -alkylcyclohexyl, phenyl, C₁ -C₄ -alkylphenyl, chlorophenyl, bromophenyl, trifluoromethylphenyl, naphthyl, trifluoromethylphenyl, naphthyl, trifluoromethyl and benzenesulphonyl which is optionally substituted by fluorine, chlorine, bromine, trifluoromethyl, C₁ -C₄ -alkyl or C₁ -C₄ -alkoxy.

Possible substituents of the alkyl radicals R₂ are, in particular, hydroxyl, cyano, formylamino, C₁ -C₄ -alkylcarbonylamino or benzoylamino which is optionally substituted by methyl, chlorine, bromine or trifluoromethyl. Possible substituents of the phenyl radicals R₂ are C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, chlorine, bromine and trifluoromethyl.

Particularly suitable dyestuffs correspond, in the form of the free acid, to the formula ##STR3## wherein R₄ denotes C₁ -C₄ -alkyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, cyanoethyl or phenyl which is optionally substituted by chlorine or methyl.

The dyestuffs of the formula (I) are prepared either by diazotising amines of the formula ##STR4## and coupling the diazotisation products with coupling components of the formula ##STR5## wherein R₁, R₂ and R₃ have the abovementioned meaning.

If R₁ denotes an optionally substituted alkyl group, an alkenyl group or an optionally substituted benzenesulphonyl radical, the dyestuffs of the formula (I) can also be prepared by alkylating, alkenylating or acylating, with optionally substituted benzenesulphonyl chlorides, hydroxyazo dyestuffs of the formula ##STR6## wherein R₂ and R₃ have the abovementioned meaning, the radical R₁ being introduced.

Examples of suitable alkylating agents are C₁ -C₄ -alkyl halides, C₁ -C₄ -dialkyl sulphates, alkylene oxides with 2 to 4 C atoms and acrylonitrile.

Suitable acylating agents are benzenesulphonic acid halides which are optionally substituted by fluorine, chlorine, bromine, methyl, ethyl or trifluoromethyl.

The dyestuffs according to the invention are suitable for dyeing natural and synthetic fibre materials, for example for dyeing wool or polyamide fibres, in level, deep red to violet shades with very good fastness to light, wet processing and perspiration. Depending on the substituents R₁, R₂ or R₃, they can be particularly suitable for dyeing polyamide fibres. For example, it is possible to prepare dyestuffs which are absorbed well onto polyamide fibres even from a neutral to weakly acid dyebath, but also to prepare those which are taken up quantitatively by the fibre only from a weakly to more strongly acid dyebath. In the same manner, their ease of combination with yellow and blue acid dyestuffs can be advantageously influenced. Polyamide fibres are understood, in particular, as those consisting of synthetic polyamides, such as ε-polycaprolactam or condensation products of adipic acid and hexamethylenediamine.

EXAMPLE 1

19.1 g of 2-amino-5-methoxy-benzotrifluoride are dissolved in 350 ml of water and 30 ml of concentrated hydrochloric acid, the solution is cooled to 0° C. and the amine is diazotised with a solution of 6.9 g of sodium nitrite in 50 ml of water. After destroying excess nitrous acid with amidosulphonic acid, the diazonium salt solution is added to a solution, cooled to 5° C., of 24.2 g of 6-amino-4-hydroxynaphthalene-2-sulphonic acid in 300 ml of dimethylformamide. The coupling is rapidly completed in the strongly acid medium. The mixture is subsequently stirred at room temperature for 2 hours. The reaction product is then filtered off and dried. 38 g of a red powder of the formula ##STR7## which dyes polyamide fibres and wool in a clear red from an aqueous solution, are obtained.

EXAMPLE 2

43 g of the dyestuff of the formula ##STR8## obtained by coupling diazotised 2-amino-5-hydroxybenzotrifluoride with 6-amino-4-hydroxynaphthalene-2-sulphonic acid, are dissolved in a mixture of 250 ml of water, 250 ml of isopropanol and 40 ml of 10% strength sodium hydroxide solution, and 10 g of propylene oxide are added in the course of 2 hours, whilst stirring. The temperature is kept at 50° C. during the addition of the propylene oxide. When the reaction has ended, which can be established by thin layer chromatography, 500 ml of water and then 70 g of sodium chloride are added, the mixture is cooled to room temperature, whilst stirring, and the dyestuff is filtered off. It has the formula ##STR9## and dyes polyamide fibres in a clear red from an aqueous solution.

EXAMPLE 3

43 g of the dyestuff of the formula ##STR10## are dissolved in 800 ml of water and 40 ml of 10% strength sodium hydroxide solution. 23 g of benzenesulphonyl chloride are added dropwise at room temperature in the course of 2 hours, whilst stirring thoroughly. The pH is kept at 8-9, if necessary by further addition of 10% strength sodium hydroxide solution. When the starting dyestuff can no longer be seen in the thin layer chromatogram, 80 g of sodium chloride are added, the mixture is further stirred for some time and the reaction product is then filtered off. After drying, 51 g of a red dyestuff of the formula ##STR11## which dyes polyamide fibres in a clear red, are obtained.

EXAMPLE 4

0.1 g of the dyestuff obtained according to Example 1 are dissolved in 100 ml of hot water. 5 ml of ammonium acetate solution are added and the mixture is diluted with cold water to a volume of 500 ml. 10 g of polyamide fibre material are introduced into this dyebath, the dyebath is heated to the boil in the course of 20 minutes, 4 ml of 10% strength acetic acid are added and the bath is kept at the boiling point for 1 hour. Thereafter, the dyed polyamide is removed from the dyebath, rinsed thoroughly with hot water and dried at 70°-80° C. A clear red dyeing is obtained.

If the diazo and coupling components listed in Table 1 are used, further valuable water-soluble dyestuffs which dye polyamide in red shades from a weakly acid or neutral bath are obtained by the process indicated in Example 1:

                                      Table 1                                      __________________________________________________________________________     Example                                                                              Diazo component     Coupling component                                   __________________________________________________________________________     5     2-Amino-5-ethoxy-benzotri-                                                                         2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       6     2-Amino-5-propoxybenzotri-                                                                         2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       7     2-Amino-5-isopropoxy-benzo-                                                                        2-Amino-8-hydroxy-                                         trifluoride         naphthalene-6-                                                                 sulphonic acid                                       8     2-Amino-5-butoxy-benzotri-                                                                         2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       9     2-Amino-5-(2-methylpropyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       10    2-Amino-5-(1-methylpropyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       11    2-Amino-5-tert.-butoxy-                                                                            2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       12    2-Amino-5-pentyloxy-benzotri-                                                                      2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       13    2-Amino-5-(3-methyl-butyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       14    2-Amino-5-allyloxy-benzotri-                                                                       2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       15    2-Amino-5-crotyloxy-benzotri-                                                                      2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       16    2-Amino-5-methallyloxy-benzo-                                                                      2-Amino-8-hydroxy-                                         trifluoride         naphthalene-6-                                                                 sulphonic acid                                       17    2-Amino-5-(2-chloroethyl)-oxy-                                                                     2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       18    2-Amino-5-(2-methoxyethyl)-oxy-                                                                    2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       19    2-Amino-5-(2-butoxyethyl)-oxy-                                                                     2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       20    2-Amino-5-(2-cyanoethyl)-oxy-                                                                      2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       21    2-Amino-5-(4-cyanobutyl)-oxy-                                                                      2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       22    2-Amino-5-trifluoromethoxy-                                                                        2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       23    2-Amino-5-(2-hydroxyethyl)-oxy-                                                                    2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic-acid                                       24    2-Amino-5-(2-hydroxybutyl)                                                                         2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       25    2-Amino-5-(2-methyl-2-hydroxy-                                                                     2-Amino-8-hydroxy-                                         propyl)-oxy-benzotrifluoride                                                                       naphthalene-6-                                                                 sulphonic acid                                       26    2-Amino-5-(2-phenylethyl)-oxy-                                                                     2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       27    2-Amino-5-cyclohexyloxy-                                                                           2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       28    2-Amino-5-(4-methylcyclohexyl)-                                                                    2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene6-                                                                  sulphonic acid                                       29    2-Amino-5-phenoxy-benzotri-                                                                        2-Amino-8-hydroxy-                                         fluoride            naphthalene-6-                                                                 sulphonic acid                                       30    2-Amino-5-(4-methylphenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       31    2-Amino-5-(2-methylphenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       32    2-Amino-5-(4-chlorophenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       33    2-Amino-5-(3-chlorophenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene6-                                                                  sulphonic acid                                       34    2-Amino-5-(2-chlorophenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-6-                                                                 sulphonic acid                                       35    2-Amino-5-(3-bromophenyl)-oxy-                                                                     2-Amino8-hydroxy-                                          benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       36    2-Amino-5-(3-trifluoromethyl-                                                                      2-Amino-8-hydroxy-                                         phenyl)-oxy-benzotrifluoride                                                                       npahthalene-6-                                                                 sulphonic acid                                       37    2-Amino-5-methoxy-benzotri-                                                                        2-Amino-8-hydroxy-                                         fluoride            naphthalene-5-                                                                 sulphonic acid                                       38    2-Amino-5-ethoxy-benzotri-                                                                         2-Amino-8-hydroxy-                                         fluoride            naphthalene-5-                                                                 sulphonic acid                                       39    2-Amino-5-butoxy-benzotri-                                                                         2-Amino-8-hydroxy-                                         fluoride            naphthalene-5-                                                                 sulphonic acid                                       40    2-Amino-5-(2-methoxyethyl)-oxy-                                                                    2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-5-                                                                 sulphonic acid                                       41    2-Amino-5-(2-hydroxyethyl)-oxy-                                                                    2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-5-                                                                 sulphonic acid                                       42    2-Amino-5-(2-cyanoethyl)-oxy-                                                                      2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-5-                                                                 sulphonic acid                                       43    2-Amino-5-trifluoromethoxy-                                                                        2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-5-                                                                 sulphonic acid                                       44    2-Amino-5-(2-phenylethyl)-                                                                         2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-5-                                                                 sulphonic acid                                       45    2-Amino-5-phenoxy-benzotri-                                                                        2-Amino-8-hydroxy-                                         fluoride            naphthalene-5-                                                                 sulphonic acid                                       46    2-Amino-5-(4-chlorophenyl)-                                                                        2-Amino-8-hydroxy-                                         oxy-benzotrifluoride                                                                               naphthalene-5-                                                                 sulphonic acid                                       47    2-Amino-5-(3-trifluoromethyl-                                                                      2-Amino-8-hydroxy-                                         phenyl)-oxy-benzotrifluoride                                                                       naphthalene-5-                                                                 sulphonic acid                                       48    2-Amino-5-methoxy-benzotri-                                                                        2-Methylamino-8-                                           fluoride            hydroxynaphthalene-                                                            6-sulphonic acid                                     49    2-Amino-5-isopropoxy-benzo-                                                                        2-Methylamino-8-                                           trifluoride         hydroxynaphthalene-                                                            6-sulphonic acid                                     50    2-Amino-5-butoxy-benzotri-                                                                         2-Methylamino-8-                                           fluoride            hydroxynaphthalene-                                                            6-sulphonic acid                                     51    2-Amino-5-phenoxy-benzotri-                                                                        2-Methylamino-8-                                           fluoride            hydroxynaphthalene-                                                            6-sulphonic acid                                     52    2-Amino-5-(4-chlorophenyl)-                                                                        2-Methylamino-8-                                           oxy-benzotrifluoride                                                                               hydroxynaphthalene-                                                            6-sulfonic acid                                      53    2-Amino-5-methoxy-benzotri-                                                                        2-Dimethylamino-8-                                         fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     54    2-Amino-5-phenoxy-benzotri-                                                                        6-Dimethylamino-8-                                         fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     55    2-Amino-5-isopropoxy-benzo-                                                                        2-Phenylamino-8-                                           trifluoride         hydroxy-naphthalene-                                                           6-sulphonic acid                                     56    2-Amino-5-phenoxy-benzotri-                                                                        2-Phenylamino-8-                                           fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     57    2-Amino-5-cyclohexyloxy-benzo-                                                                     2-Phenylamino-8-                                           trifluoride         hydroxy-naphthalene-                                                           6-sulfonic acid                                      58    2-Amino-5-methoxy-benzotri-                                                                        2-β-Hydroxyethyl-                                     fluoride            amino-8-hydroxy-                                                               naphthalene-6-                                                                 sulphonic acid                                       59    2-Amino-5-phenoxy-benzotri-                                                                        2-β-Hydroxyethyl-                                     fluoride            amino-8-hydroxy-                                                               naphthalene-6-                                                                 sulfonic acid                                        60    2-Amino-5-methoxy-benzotri-                                                                        2-Butylamino-8-                                            fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     61    2-Amino-5-butoxy-benzotri-                                                                         2-Butylamino-8-                                            fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     62    2-Amino-5-phenoxy-benzotri-                                                                        2-Butylamino-8-                                            fluoride            hydroxy-naphthalene-                                                           6-sulphonic acid                                     63    2-Amino-5-(4-chlorophenyl)-                                                                        2-Butylamino-8-                                            oxy-benzotrifluoride                                                                               hydroxy-naphthalene-                                                           6-sulphonic acid                                     64    2-Amino-5-methoxy-benzotri-                                                                        2-Cyclohexylamino-                                         fluoride            8-hydroxy-naphtha-                                                             lene-6-sulphonic                                                               acid                                                 65    2-Amino-5-phenoxy-benzotri-                                                                        2-Cyclohexylamino-                                         fluoride            8-hydroxy-naphtha-                                                             lene-6-sulphonic                                                               acid                                                 66    2-Amino-5-(4-chlorophenyl)-                                                                        2-Cyclohexylamino-                                         oxy-benzotrifluoride                                                                               8-hydroxy-naphtha-                                                             lene-6-sulfonic                                                                acid                                                 67    2-Amino-5-methoxy-benzotri-                                                                        2-(2,4-Dimethyl-                                           fluoride            phenyl)-amino-8-                                                               hydroxy-nahthalene-                                                            6-sulphonic acid                                     68    2-Amino-5-phenoxy-benzotri-                                                                        2-(2,4-Dimethyl-                                           fluoride            phenyl)-amino-8-                                                               hydroxy-naphthalene-                                                           6-sulphonic acid                                     69    2-Amino-5-(2-hydroxyethyl)-                                                                        2-(2,4-Dimethyl-                                           oxy-benzotrifluoride                                                                               phenyl)-amino-8-                                                               hydroxy-naphthalene-                                                           6-sulphonic acid                                     70    2-Amino-5-(4-tert.-butyl-                                                                          2-Amino-8-hydroxy-                                         phenyl)-oxy-benzotrifluoride                                                                       npahthalene-6-                                                                 sulphonic acid                                       71    2-Amino-5-(4-methylmercapto-                                                                       2-Amino-8-hydroxy-                                         phenyl)-oxy-benzotrifluoride                                                                       naphthalene-6-                                                                 sulphonic acid                                       72    2-Amino-5-(1-naphthyloxy)-                                                                         2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       73    2-Amino-5-(2-naphthyloxy)-                                                                         2-Amino-8-hydroxy-                                         benzotrifluoride    naphthalene-6-                                                                 sulphonic acid                                       __________________________________________________________________________

Table 2 gives further dyestuffs which dye polyamide in red shades and which have been obtained by alkylating or acylating the dyestuff of the formula ##STR12## on the OH group of the benzene ring, using the alkylating or acylating agents indicated in the Table.

                  Table 2                                                          ______________________________________                                         Example Alkylating or acylating agent                                          ______________________________________                                         74      Dimethyl sulphate                                                      75      Diethyl sulphate                                                       76      4-Methylbenzenesulphonic acid methyl ester                             77      Ethylene oxide                                                         78      Propylene oxide                                                        79      1,2-Butylene oxide                                                     80      Styrene oxide                                                          81      2-Chloroethanol                                                        82      Benzyl chloride                                                        83      Acrylonitrile                                                          84      Phenethyl bromide                                                      85      Allyl bromide                                                          86      4-Methyl-benzenesulphonyl chloride                                     87      2-Methylbenzenesulphonyl chloride                                      88      3-Methylbenzenesulphonyl chloride                                      89      4-Ethylbenzenesulphonyl chloride                                       90      4-Chlorobenzenesulphonyl chloride                                      91      4-Bromobenzenesulphonyl chloride                                       92      4-Fluorobenzenesulphonyl cholride                                      93      3-Trifluoromethylbenzenesulphonyl chloride                             94      4-Methoxybenzenesulphonyl chloride                                     95      2,4-Dichlorobenzenesulphonyl chloride                                  96      4-Isopropylbenzenesulphonyl chloride                                   97      4-tert.-Butylbenzenesulphonyl chloride                                 98      4-Butoxybenzenesulphonyl chloride                                      ______________________________________                                     

We claim:
 1. A water-soluble monoazo dyestuff which, in the form of the free acid, corresponds to the formula ##STR13## wherein R₁ denotes alkyl alkyl mono-substituted by chlorine, hydroxyl, C₁ to C₄ alkoxy, cyano, phenyl or tolyl, cyclohexyl cyclohexyl substituted by C₁ -C₄ -alkyl, phenyl C₁ -C₄ -alkyl phenyl, chlorophenyl, bromophenyl, trifluoromethylphenyl or napthyl, alkenyl or benzenesulphonyl benzenesulphonyl substituted by fluorine, chlorine, bromine, trifluoromethyl, C₁ -C₄ -alkyl or C₁ -C₄ -alkoxy,R₂ denotes hydrogen, C₁ -C₄ -alkyl C₁ -C₄ -alkyl substituted by hydroxyl, cyano, formylamino, C₁ -C₄ alkylcarbonylamino or benzoylamino, C₁ -C₄ -alkyl- carbonylamino or benzoylamino; substituted by methyl, chlorine, bromine or trifluoromethyl; cyclohexyl or phenyl, cyclohexyl or phenyl substituted by C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, chlorine, bromine, or trifluoromethyl and R₃ denotes hydrogen or C₁ -C₄ -alkyl.
 2. An azo dyestuff according to claim 1, wherein the sulphonic acid group is in the m-position or p-position relative to the hydroxyl group.
 3. An azo dyestuff according to claim 1, whereinR₁ denotes C₁ -C₈ -alkyl, C₁ -C₈ -alkyl monosubstituted by chlorine, hydroxyl, C₁ -C₄ -alkoxy, cyano, phenyl or tolyl, C₂ -C₄ -alkenyl, cyclohexyl, C₁ -C₄ -alkylcyclohexyl, phenyl, C₁ -C₄ -alkylphenyl, chlorophenyl, bromophenyl, trifluoromethylphenyl, naphthyl, trifluoromethyl or benzenesulphonyl or benzenesulphonyl substituted by fluorine, chlorine, bromine, trifluoromethyl, C₁ -C₄ -alkyl or C₁ -C₄ -alkoxy, R₂ denotes hydrogen or C₁ -C₄ -alkyl, C₁ -C₄ -alkyl substituted by hydroxyl, cyano, formylamino, C₁ -C₄ -alkylcarbonylamino or benzoylamino, C₁ -C₄ -alkylcarbonylamino or benzoylamine; substituted by methyl, chlorine, bromine or trifluoromethyl, or phenyl or phenyl substituted by C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, chlorine, bromine or trifluoromethyl and R₃ denotes hydrogen or C₁ -C₄ -alkyl.
 4. An azo dyestuff according to claim 1 which, in the form of the free acid, corresponds to the formula ##STR14## wherein R₄ denotes C₁ -C₄ -alkyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, cyanoethyl or phenyl or phenyl substituted by chlorine or methyl. 